Volume 10 Issue 8, August 2011

As complex new materials such as nanoparticles increasingly make their way into commercial products, regulatory frameworks need to overcome a number of key challenges to remain fit for purpose.

Stem cells that are cultured in the laboratory differentiate in response to the mechanical properties of the substrate and its topography. It is now shown that mesenchymal stem cell multipotency is prolonged when the cells are cultured on a surface patterned with an ordered arrangement of nanoscale pits.

A single nanodevice that detects the presence of a single molecule would perhaps be the ultimate sensor. The demonstration of hydrogen sensing based on a single gold nanoaerial brings that possibility nearer.

Living cells regulate their area through active mechanisms, which often lead to the fusion and fission of lipid vesicles. It is now found that bilayers adhered to elastic substrates can also adjust their area passively, in response to applied lateral strains.

The design of structures of organic nanoporous crystals has been hampered by the difficulty of placing functional moieties in a predictive manner. A modular strategy based on prefabricated organic nanocages having directional chiral interactions that self-assemble into the predicted crystals circumvents this problem.

A new design for elastic metamaterials that can behave either as liquids or solids over a limited frequency range may enable new applications based on the control of acoustic, elastic and seismic waves.

The main challenges to face before graphene can become part of realistic applications were discussed at a recent dedicated meeting.

The thermal properties of nanostructures have become a fundamental topic owing to the necessity of heat removal in increasingly smaller electronic devices. Carbon allotropes present a range of intriguing thermal features, with the thermal conductivity spanning five orders of magnitude at room temperature. The topic is reviewed here with particular emphasis on graphene, which exhibits the highest thermal conductivity observed.

Materials with zero refractive index show unusual waveguiding properties and, for example, can squeeze light through narrow passages. It is now suggested that such properties can also be realized in a non-metallic photonic crystal. Furthermore, such photonic crystals can also show a Dirac point in the band structure—offering further possibilities, such as guiding waves unperturbed around bends and obstacles.

The energy and power density of lithium-ion batteries depends to a large extent on storing lithium by incorporation in the crystal structure of the cathode. The reason that LiFePo₄ functions as a cathode at a reasonable rate is now explained theoretically by the availability of a single phase-transformation path at low overpotential.

The electronic properties of inorganic devices such as memristors can be used to simulate neurological behaviour. In particular, ionic and electronic effects in a silver sulphide device are now shown to mimic short- and long-term synaptic functions.

The low-temperature solution growth of ZnO nanostructures could enable the bottom-up fabrication of integrated electronic devices, but controlling their morphology has been challenging. It is now shown that the geometry of hydrothermally synthesised ZnO nanowires can be tuned precisely if the growth of selected crystal faces is inhibited by the competitive adsorption of non-zinc ions.

The in vivo optical detection of bacterial infections requires highly specific imaging probes with small affinity to mammalian tissue. It is now shown that fluorescent dyes that are conjugated to maltohexaose can be internalized rapidly via the bacteria-specific maltodextrin transport pathway, enabling the in vivo imaging of Escherichia coli down to 10⁵ colony-forming units.

The advance of nuclear technologies is strongly linked to the development of enhanced radiation-tolerant materials. Indentation measurements of irradiated copper nanopillars now demonstrate that in situ testing can offer a convenient method to determine bulk-like yield strengths and simultaneously identify deformation mechanisms.

Neutron scattering and first-principles calculations show that the small thermal conductivity of PbTe is due to anharmonic coupling between the acoustic phonon modes and the optical ferroelectric ones. The results provide a microscopic picture of why many good thermoelectrics are found near a ferroelectric lattice instability.

The ability to withstand shear is one of the properties that distinguishes a solid from a liquid. The proposal of an elastic metamaterial that in one direction only supports compressional waves, and therefore is fluid-like, and in the other supports compressional as well as shear waves represents a hybrid between fluids and solids that may lead to new applications.

Resistive switching is a promising technology to replace current non-volatile memory technologies such as flash. The demonstration of a fast, stable and highly scalable resistive-switching memory device represents a significant advance towards the practical implementation of this technology.

Plasmonic resonances are widely used for sensing applications. The plasmon resonance of a single nanoantenna structure is now used to detect changes in the dielectric properties of a nearby palladium nanoparticle exposed to hydrogen gas, enabling highly sensitive sensing in ultrasmall volumes. The approach can be easily extended to other sensing and catalysis schemes.

On standard tissue culture platforms, mesenchymal stem cells tend to spontaneously differentiate with the loss of multi-lineage potential. Now, a robust and reproducible nanotopographical platform has been shown to maintain stem cell phenotype and promote stem cell growth over several months whilst implicating mechanisms for the observed stem cell behaviour